MD Bookmarks: Show toolbar overlay when multiple items are selected

chrome/app/bookmarks_strings.grdp

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Bookmarks specific strings (included from generated_resources.grd). -->
 <grit-part>
   <!-- Begin of Bookmarks Bar strings-->
   <if expr="not is_android">
     <!-- The following two strings are shown when the user has no bookmarks yet. -->
     <message name="IDS_BOOKMARKS_NO_ITEMS" desc="Text shown when the user has no bookmarks">
       For quick access, place your bookmarks here on the bookmarks bar.
     </message>
     <message name="IDS_BOOKMARK_BAR_IMPORT_LINK" desc="text shown for importing ">
@@ skipping 392 matching lines @@
   </message>
   <message name="IDS_MD_BOOKMARK_MANAGER_MENU_RENAME" desc="Title of the bookmark list dropdown menu item that renames folders.">
     Rename
   </message>
   <message name="IDS_MD_BOOKMARK_MANAGER_MENU_SORT" desc="Title of the bookmark toolbar dropdown menu item that sorts bookmarks by title.">
     Sort by title
   </message>
   <message name="IDS_MD_BOOKMARK_MANAGER_NO_SEARCH_RESULTS" desc="Text on the bookmarks list that indicates that no bookmarks or folders match the search.">
     No search results found
   </message>
+  <message name="IDS_MD_BOOKMARK_MANAGER_ITEMS_SELECTED" desc="Label displayed in bookmark manager toolbar telling the user how many items they have selected.">
+    <ph name="NUMBER_OF_ITEMS_SELECTED">$1</ph> selected
+  </message>
   <message name="IDS_MD_BOOKMARK_MANAGER_TITLE" desc="Title of the bookmark manager window.">
     Bookmarks
   </message>
   <!-- End of material design Bookmarks Manager strings. -->
 
   <!-- Begin of Bookmarks Menu (in the Main Menu) strings. -->
   <message name="IDS_BOOKMARKS_MENU" desc="The title of the Bookmarks menu in the Main menu and in the Mac menu bar.">
     &amp;Bookmarks
   </message>
   <if expr="not use_titlecase">
@@ skipping 18 matching lines @@
   </if>
   <!-- End of Bookmarks Menu (in the Main Menu) strings. -->
 
   <!-- Begin of Bookmark Star button strings. -->
   <message name="IDS_TOOLTIP_STARRED" desc="The tooltip shown when you hover the star button in the right side of the location bar and the current page is bookmarked.">
     Edit bookmark for this page
   </message>
   <!-- End of Bookmark Star button strings. -->
 
 </grit-part>